The present invention generally relates to a joint construction for an ignition system and more particularly, to a joint construction between a rodlike high-voltage terminal provided at a distal end of an ignition coil or an ignition cable of an internal combustion engine and a tubular electrical conductor, in which the high-voltage terminal is connected to a spark plug through the electrical conductor.
Japanese Utility Model Laid-Open Publication No. 64-8580 (1989) discloses an ignition system for connecting an ignition coil and a spark plug through an electrical conductor as shown in FIG. 1. In FIG. 1, an insulator 4 is mounted in a hole 3 formed on a cylinder head 2 of an engine 1 and an electrical conductor 5 is fitted into a bore of the insulator 4. A terminal 6 provided at an upper portion of the electrical conductor 5 is urged by a spring 7 so as to be brought into contact with a high-voltage terminal 9 of an ignition coil 8 inserted into inserted into an upper portion of the insulator 4. Meanwhile, a terminal 10 provided at a lower portion of the electrical conductor 5 is urged by a spring 11 so as to be brought into contact with a terminal 13 of a spark plug 12 inserted into a lower portion of the insulator 4.
In this known ignition system, since electrical sealing property between the spark plug 12 and the insulator 4 is required to be upgraded in response to rise of required voltage, the bore of the insulator 4 is reduced in diameter so as to powerfully clamp an insulator portion 12a of the spark plug 12.
However, in the known ignition system, the ignition coil 8 and the electrical conductor 5 are adapted to be separated from each other functionally. Therefore, if the ignition coil 8 is lifted upwardly with a hand when the ignition system is removed from the engine 1, large clamping force applied to the spark plug 12 by the insulator 4 removes the ignition coil 8 from the insulator 4 before the insulator 4 is separated from the spark plug 12. As a result, the insulator 4, the electrical conductor 5, etc. remain in the hole 3 of the engine 1 undesirably.
In order to eliminate this drawback, it may be considered that the ignition coil 8 is clamped by the insulator 4 more powerfully. However, in this case, since force for inserting the ignition coil 8 into the insulator 4 is also increased, such an inconvenience is incurred that working efficiency for inserting the ignition coil 8 into the insulator 4 deteriorates. Alternatively, if the ignition coil 8 is bonded to the electrical conductor 5 and the insulator 4, such a problem arises that these element 4, 5 and 8 cannot be replaced with new ones separately.